There has been increasing concern over the upsurge in skin cancer in the United States due to excessive exposure to the sun. In particular the amount of UVA exposure (320-400 nm of the solar spectrum band) is increasing since most sunscreens effectively only block UVB radiation (290-320 nm). Users continue to stay in the sun for excessive periods without seeing any immediate harmful effects of UVA radiation which are more long term in nature.
As used in the specification, the term UV covers the ultraviolet region (290-400 nanometers (nm)) of the solar spectrum. The term infrared (IR) covers the range above 760 nm.
The goal of a successful sunscreen agent must be to protect the user from both UVA and UVB radiation with minimal side effects. This has been a particularly difficult problem when attempting to protect sensitive areas, such as the area around the eyes or lips. While chemical sunscreen compositions in the form of creams and lotions are known, they are irritating when applied to such sensitive areas. If the user avoids too close a contact with such areas, needed protection is not secured.
In addition to chemical sunscreens, the use of physical sunscreens is known in the art. Such sunscreens comprise particles of relatively physiolocially inert sunblocks or sunscreens, such as kaolin, talc, zinc oxide and titanium dioxide suspended in a cream or lotion. However, such physical sunblocks have significant disadvantages. They in general exhibit lower effectiveness in absorbing UV radiation as compared to many chemical sunblocks. When their concentration is increased to promote greater effectiveness, an undesirable white layer appears on the skin which most users find objectionable. When using such physical sunscreen compositions to protect the eyes, one may assume a "racoon like" appearance clearly in conflict with the attractive tanned look sought by the average person.
Recent modifications of conventional chemical and physical sunscreens are disclosed in U.S. Pat. No. 5,223,250 to Mitchell and Mitchnick, the relevant portions of which are hereby incorporated by reference in this specification. Column 3 of this patent describes the use of "micronized" titanium dioxide or "large surface area" particles having smaller particle diameters than conventional titanium dioxide. Such micronized titanium dioxide particles are smoother and less occlusive and thus provide a more cosmetically acceptable formulation. However, they still exhibit a low sunblock effectiveness. U.S. Pat. No. 5,223,250 also discloses an alternative sunblock formulation wherein a chemical UV additive capable of absorbing ultraviolet light radiation is incorporated into commercially available small plastic particles (0.01-100 microns) during their formation (column 10 line 42 through column 11 line 47).